Please refer to FIG. 1, it shows the schematic circuit diagram of a clamping and energy recycle circuit of the prior art. In which, diodes Dr1, Dr2, and capacitor C1 form a clamping circuit of the rectifying diodes D1 and D2. Capacitor C2, inductor L2, switch element Q1, and diode Dr3 form an energy recycle circuit. A constant-current output would be required by certain power supply even when the output capacitor is in the abnormal operation, but the problem regarding the voltage spikes during the reverse recovery of the diode still exists. To keep the voltage across the capacitor C1 unchanged, the included energy recycle circuit must be operated, and the duty ratio of the energy recycle circuit is proportional to the voltage across the capacitor C1. Since the duty ratio of the energy recycle circuit is relatively high, and the voltage across the capacitor Cout is relatively low due to the output is in the abnormal operation, such that the inductor L2 could not be reset. Thus, the energy recycle circuit would be damaged, and then the rectifying diodes, D1 and D2, would be damaged too.
Please refer to FIGS. 2, 3 and 4, which are the schematic circuit diagrams of three typical clamping and energy recycle circuits of the prior arts. All these circuits face the same problem, that is, when the output (Cout) is in the abnormal operation, the inductor L1 could not be reset. In FIG. 2, the capacitor C1 is electrically connected to the power supply in parallel, and is electrically connected to the output capacitor Cout in series. In which, the possible voltage spikes are clamped by the capacitor C1, and the energy from the capacitor C1 is transferred into the output capacitor Cout through an energy recycle circuit. The energy recycle circuit includes an inductor L1, a switch element Q1, and a diode D1. The output capacitor Cout, the diode D1, and the inductor L1 are connected in series to form a loop. In FIG. 3, the capacitors C1 and Cout are electrically connected to each other in series, and are electrically connected to the power supply in parallel. In which, the possible voltage spikes are clamped by the capacitors C1 and Cout electrically connected in series, and the energy from the capacitor C1 is transferred into the output capacitor Cout through the above-mentioned energy recycle circuit. In FIG. 4, the possible voltage spikes are clamped by the capacitor C1, and the energy from the power source is transferred into the output capacitor Cout through the above-mentioned energy recycle circuit. The aforementioned voltage spikes are caused by the reverse recovery of the diode or the switch element.
Keeping the drawbacks of the prior arts in mind, and employing experiments and research full-heartily and persistently, the apparatus for protecting the boost converter in the abnormal operation is finally conceived by the applicants.